With the ever increasing world wide consumption of fossil fuels, there has been an ever increasing interest in alternative energy options. Considerable interest has now been focused on the use of ethanol.
Ethanol has been found to have widespread application in beverages and food, as an industrial chemical, as a gasoline additive, and now, even more importantly, as a fuel or gasoline replacement. Ethanol produces less toxic air emissions such as carbon monoxide, CO, than the hydrocarbon fossil fuels currently used. Furthermore, ethanol has the advantage of being a renewable resource, as opposed to fossil fuel oil which is finite. Use of ethanol can also reduce the nation's dependence on these finite and largely foreign fossil fuel sources. However, efficiently producing ethanol in sufficient quantities remains a concern.
Various sources and methods of ethanol production have been attempted to date. There has been an increasing interest in the use of cellulose waste or by-products as a source of ethanol production because these materials are often simply disposed of. Examples of such materials include the waste or by-products produced as a result of harvesting agricultural crops such as the stalks, hulls or husks from legumes, or waste from cows or bovines. After harvesting, for example, the unwanted hulls and husks of legumes may be used as animal feed or field spread for easy disposal. Animal wastes may also be field spread for easy disposal. It has become desirable to employ such cellulose by product materials for conversion to ethanol, particularly in light of the rising cost of fossil fuels.
Cellulose is a polymer of D-glucose molecules linked together via β-1,4 linkages. Prior to fermentation, these polymers are cleaved or depolymerized to form simple sugars. This process is sometimes referred to in the art as saccharification.
Cellulose, however, is very resistant to cleavage. Thus, it can be challenging to accomplish the conversion in an efficient, economic manner so as to produce sufficient quantities of sugars which can then be fermented to ethanol. However, once cellulose is converted to fermentable sugars such as glucose, the resulting sugar is easily fermented to ethanol using yeast. Thus, the difficult challenge of the process is to convert the cellulose to yeast fermentable sugars such as glucose.
Commonly employed methods of saccharification include acidic and enzymatic hydrolysis, and mechanical degradation, the latter typically being employed in combination with one of the other methods.
Acid hydrolysis involves the use of either concentrated or diluted mineral acids. In concentrated form, the acids can produce high yields of fermentable sugars such as glucose, are expensive and cause difficulties for disposal of the waste acid material. To improve the overall yield of acid hydrolysis using diluted acids, pretreatment of the cellulose has been employed, and/or enzymatic hydrolysis. Pretreatment involves mechanically and/or chemically treating the cellulose in order to break down the integrity of the fiber structure of the cellulose in order to make it more susceptible to attack by cellulose enzymes.
Mechanical treatment may involve pressure, grinding, milling agitation, shredding, compression/expansion, etc. Sonification or ultrasound are commonly employed in pretreatment of cellulose. Chemical methods involve the use of steam, acids or solvents. Many such pretreatment processes may leave a muddy pulp and undissolved solids.
Adding enzymes, on the other hand, improves the efficiency of the process, but significantly increases the cost of production making it economically inefficient for large scale production operations.
A further complication is that yeast have a limited ability to ferment sugars other than glucose. Many methods of converting cellulose to glucose, such as acid hydrolysis, produce sugars, in addition to glucose, such as xylose in rather large quantities, which are not yeast fermentable which further decreases the efficiency of the process.
There is a continuing need for efficiently and economically converting cellulose to yeast fermentable sugars which can then be fermented to ethanol.
The art referred to and/or described above is not intended to constitute an admission that any patent, publication or other information referred to herein is “prior art” with respect to this invention. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 C.F.R. §1.56(a) exists.
All US patents and applications and all other published documents mentioned anywhere in this application are incorporated herein by reference in their entirety.
Without limiting the scope of the invention a brief summary of some of the claimed embodiments of the invention is set forth below. Additional details of the summarized embodiments of the invention and/or additional embodiments of the invention may be found in the Detailed Description of the Invention below.
A brief abstract of the technical disclosure in the specification is provided as well only for the purposes of complying with 37 C.F.R. 1.72. The abstract is not intended to be used for interpreting the scope of the claims.